The Remote Equivalent Copy (REC) function is known as one of methods of backing up of data of a storage device in a storage system including multiple storage devices.
The REC function copies data of one device into another remote device, and more specifically forwards and copies data in the logical unit of a storage device into the logical unit of another storage unit. Upon completion of the copying, the logical unit of the destination device is kept to be equivalent to that of the source device. In other words, updating of data in the logical unit of the source device is reflected in the logical unit of the destination device, so that data in the both logical units are kept to be equivalent.
The scheduling of data forwarding under the REC function is accomplished by a controller of the source storage device. The scheduling carries out each forwarding process on data of a predetermined data size (e.g., 256 KB) at a multiplicity representing the number of data forwarding processes that may be simultaneously carried out.
For each of the remote lines that connect storage devices, a maximum line multiplicity is set to be the upper limit of the umber of data forwarding processes that the remote line may optimally handle on the basis of the data (e.g., the performance line speed, the line response delay time) of the remote line.
Each storage device carries out data forwarding within the maximum line multiplicity. If a number of copy sessions are present, the copy sessions are scheduled to be evenly performed among the storage devices.    [Patent Literature 1] Japanese Laid-Open Patent Publication No. 2005-275537
However, a conventional method for remote copying using the REC function has a problem of: if multiple storage devices are connected to a single remote line, each storage device not grasping the multiplicities of data forwarding processes by the other storage devices. Accordingly, a remote line may be scheduled to carry out copy sessions beyond the maximum line multiplicity.
Accompanying drawing FIG. 18 is a diagram illustrating remote copying in a conventional storage system. In the example of FIG. 18, a number (four in the example of FIG. 18) of storage devices 300-0 through 300-3 are connected to a remote line 310. The maximum line multiplicity of the remote line 310 is assumed to be 16.
In the conventional storage system of FIG. 18, the storage device 300-2 carries out data forwarding to storage devices 300-0 and 300-1 both at multiplicity of 8, considering the maximum line multiplicity of 16 set for the remote line 310. Concurrently, the storage device 300-3 carries out data forwarding to the storage device 300-0 at a multiplicity of 16.
Consequently, copy sessions are scheduled at a multiplicity of 32 for the remote line 310, which is set to have a maximum line multiplicity of 16, so that the remote line 310 is overloaded. In other words, copy sessions are not properly scheduled for the remote line 310.